The present invention relates to developer storage and dispensing apparatus. More specifically, the present invention is directed to developer dispensing apparatus for a developer station in an automatic electrostatographic printing machine.
Generally, in the process of electrostatographic printing, a photoconductive insulating member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive insulating layer is thereafter exposed to a light image of an original document to be reproduced. This records an electrostatic latent image on the photoconductive member corresponding to the information areas contained within the original document. Alternatively, in a printing application, the electrostatic latent image may be created electronically by exposure of the charged photoconductive layer by an electronically controlled laser beam. After recording the electrostatic latent image on the photoconductive member, the latent image is developed by bringing a developer material charged of opposite polarity into contact therewith. In such processes, the developer material may comprise a mixture of carrier particles and toner particles or toner particles alone. Toner particles are attracted to the electrostatic latent image to form a toner powder image which is subsequently transferred to copy sheet and thereafter permanently affixed to copy sheet by fusing.
In such automatic printing machines, the toner material is consumed in a development process and must be periodically replaced within the development system in order to sustain continuous operation of the machine. Various techniques have been used in the past to replenish the toner supply. Initially, new toner material was added directly from supply bottles or containers by pouring into the dispensing apparatus fixed in the body of the automatic reproducing machine. The addition of such gross amounts of toner material altered the triboelectric relationship between the toner and the carrier in the developer resulting in reduced charging efficiency of the individual toner particles and accordingly a reduction of the development efficiency when developing the electrostatographic latent image on the image bearing surface. In addition, the pouring process was both wasteful and dirty in that some of the toner particles became airborne and would tend to migrate into the surrounding area and other parts of the machine. Accordingly, separate toner or developer hoppers with a dispensing mechanism for adding the toner from the hopper to the developer apparatus in the automatic printing machines on a regular or as needed basis have been provided. In addition, it has been common practice to provide replenishing toner supplies in a sealed container which, when placed in the automatic printing machine, can be automatically opened to dispense toner. In such systems as necessary, the developer may be dispensed from the container relatively uniformly. Further, difficulty may arise in uniformly dispensing the developer, in that with a large mass of toner particles, which frequently are somewhat tacky, the particles may tend to agglomerate, become compacted, and form a bridging structure in the toner container. In addition, with the use of removable or replaceable developer cartridges, and due to the relative high cost of the developer contained therein, it is desirable to remove as much of the developer as possible during the dispensing operation from the cartridge so that only a minimal quantity of developer is not consumed in the dispensing operation and subsequently utilized in the formation of images. Excessive quantities of developer undispensed and remaining in an empty developer cartridge will increase the cost per copy to the consumer.
Various devices have been used to overcome the above-noted problems. For example, in U.S. Pat. No. 4,739,907 a spring auger is provided in a dispenser apparatus which is replaceable within the machine. In this system, the auger is driven about one end in rotation to move toner. Problems can develop, however, when such an auger spring is used to transport toner along nonlinear paths. For example, it may be desirable to transport toner along a tortuous path within the electrostatographic printing apparatus. A single metal wire auger spring, as used in the art for dispensing toner, will prematurely break when used at large angles.